Conventional agricultural balers such as large rectangular balers are designed for making bales from a multitude of crops in a wide range of circumstances. The operator tends to maximize the density of the bales thereby increasing the tension in the strands of binding material which are tied around the crop material in the baling chamber. Hence the forces on the tying mechanism increase accordingly and the system becomes more prone to failure, e.g. because one of the strands slips out of a knotter, or because the strand itself breaks. The adjustment of the various components of the tying mechanism becomes very critical and misties cannot always be precluded.
In case the operator timely detects an anomaly of the system, i.e. well before the bale is ejected out of the baler, he can intervene and restore the loop around the bale manually without substantial loss of baling time. He may also prevent that components of the knotter system from becoming damaged when a knot is not properly released from the bill hook. Hence it is paramount that misties are timely indicated to the operator.
Several systems have been developed for monitoring the tying mechanism in balers. U.S. Pat. No. 4,196,661, issued Apr. 8, 1980 in the name of George Yatcilla et al, and No. 4,765,235, Aug. 23, 1988 in the name of Thomas G. Schragg et al, describe a system in which the position of the slack take-up arms of the knotters is monitored. When broken, the strand of binding material will no longer retain the arm which rises to its upper position which will be detected by the operator. However, when a completed knot fails to fall off the bill hook or when the upper strand is caught in some knotter component, the strand will remain stretched and no upward movement of the arm will be perceived. Such misties will pass undetected.
The mistie detection system according to European Patents No. EP 0,294,075 and No. EP 0,294,078, involves monitoring the closed loop after the knotter has cycled. When no closed loop is sensed a mistie signal is generated. Such system rapidly indicates a failure of a knot in a completed bale, but will not react to a breakage of a strand which still has to be tied around the next bale. Hence the operator misses the opportunity to reinstall the twine before the next knotting cycle, which would have constituted the most efficient remedy. Now he has to wrap a complete new loop around the completed bale.
Twine breakage may be detected by a mistie detection system according to DD 208,748, but herein the switch on the trip arm prevents mistie signals from being passed on to the operator before the new bale is almost completed. A failure of the knotting system will be indicated only at a very late stage.
Therefore it is an object of the present invention to overcome the problems indicated above and to provide a mistie detector system which on the one hand detects both broken and jammed strands and on the other hand provides a warning to the operator shortly after the occurrence of the failure.